The present invention relates generally to the field of heat sealing machines, and more particularly, to the field of heat sealing machines used in the production of plastic cased storage batteries.
Typically, during the construction of a plastic cased storage battery, various internal elements of the battery are fitted into a polypropylene battery case prior to sealing a polypropylene battery cover to that case. Unlike other general heat sealing operations, the seals which are produced around the edges of the case and between the battery cell partitions and the underside of the battery cover must be unusually strong and liquid tight. A failure in the seal at any point along the top edge of the battery is likely to result in the leakage of sulfuric acid into the environment, whereas a failure in the seal between inter-cellular partitions and the battery cover is likely to result in a phenomenon known as acid pumping, which will eventually cause the failure of that storage battery. Finally, the seals which are produced between the battery cover and the battery case must be of sufficient strength to withstand extreme vibration and great stress, not only due to the weight of the lead battery plates and acid electrolyte, but also by reason of the intended end uses to which storage batteries are normally subjected.
For the above described reasons, it is of particular importance to obtain even melting of those portions of the battery cover and polypropylene case which are to form the heat seal between those two elements. Normally, this operation is accomplished by simultaneously melting portions of the polypropylene battery cover and polypropylene case using a single, heated platen, and then by quickly removing the platen and pressing the case and battery cover together under pressure for a sufficient length of time to allow the hardening of the melted material.
Referring now to FIG. 1, one such prior art machine for accomplishing the sealing of polypropylene battery cases to polypropylene covers is shown. Generally, this machine is located along a roller conveyor assembly line, along which various other battery assembly operations are performed. The machine shown in FIG. 1 is therefore a small segment of this battery assembly line along which many other operations are performed.
Generally, batteries, onto which have been loosely fitted battery covers, are introduced into said machine along roller conveyor 114. Various controls which are regulated from control panel 124, which is supported on control base 122, regulate the incoming rate of the battery cases and covers to be sealed, as well as provide stop means for precisely locating one or more batteries along the roller conveyor 114 under the head 100 and substantially adjacent to the conveyor lifter 116.
Referring now to FIG. 7, which is a side view of the prior art machine shown in perspective in FIG. 1, it can be seen that one or more batteries are to be located directly under vacuum head 150. Conveyor lifter 116 then elevates the portion of the conveyor on which the battery or batteries are resting, so as to bring in mating engagement with the vacuum head 150 the polypropylene or other plastic battery covers which were loosely fitted on the top of the polypropylene battery cases. Vacuum means within the vacuum head 150 then retain the battery covers as the conveyor lifter returns to its original "down" position, thereby separating the polypropylene battery cover from the polypropylene battery case by an amount sufficient to allow the introduction of a heated platen or platens 130. The platen is introduced into the space between the battery cover and battery case by the movement of the carriage 110 on which the platen 130 is mounted, said carriage automatically sliding along a pipe slide 142, and being set by various controls to stop at a point at which the platens are pecisely aligned under and over the battery cover and the battery case respectively. The conveyor lifter 116 then again elevates the battery case to clamp the hot platen between the upper portion of a case and the lower portion of a battery cover. The hot platen is so inscribed as to melt those portions of the battery cover and battery case to be sealed, said melting taking place during this clamping step and prior to the conveyor lifter 116 returning to its normal down position. Once the conveyor lifter 116 has returned to its down position, the carriage returns to its original position wherein said heated platen no longer interferes in the joining of the battery cover and battery case, which is accomplished by a third lifting of the battery case by the conveyor lifter 116 and maintenance of the battery case and battery cover in the joined position for a sufficient length of time to allow for the setting of the melted portions of those elements. Once the melted portions of the elements have set, the conveyor lifter returns to its original position and the battery case or cases are allowed to travel along the roller conveyor 114 to the next station in the production line.
As seen in FIGS. 1 and 7, various support means are provided for the roller conveyor 114, the carriage 110 and the head 100. In particular, the control base 122, the lifter base 118, the conveyor base 120, and the carriage base 112, provide the primary support for the roller conveyor 114 and the carriage 110. The head 100 is supported by supporting shafts 102, which engage the carriage base 112 and are reinforced by cross braces 106. In order to accommodate battery cases and covers of different heights, the head 100 is vertically adjustable by means of head adjustment shaft 104, which is actuated by head adjustment shaft handle 108.
Since it is common practice to heat seal two or more batteries at one time, the size of the platen 130 to be employed in the above described heat sealing operation is quite large. Because of the demanding requirements of the seals to be made in this heat sealing operation, and because of the large sealing area along which effective seals must be produced, heretofore great difficulty has been encountered in properly aligning the platen 130 so that its upper and lower sealing surfaces are precisely parallel to the upper and lower surfaces of the battery case and battery cover respectively. In order to facilitate the adjustment and alignment of the platen 130, various adjustment means have traditionally been provided to allow the adjustment in mounting of the platen 130 with respect to the carriage 110.
As shown in FIG. 1, these mounting and adjusting means comprise platen brackets 134, platen mounting plates 144 and carriage mounting plates 138. Traditionally, these mounting and adjusting means have comprised a plurality of set screws, slides, and other adjustable fastening means, which have made it possible to bolt the platen 130 to the carriage 110 in the desired position.
Nonetheless, great difficulty has been encountered in rapidly and accurately changing and aligning platens which are to be used in the heat sealing operation. Heretofore, it has been necessary to allocate between 2 and 7 hours of time to change and align a single platen. This amount of time is necessitated primarily by reason of the high temperatures and high heat capacity of the platen 130 which must be employed in the battery sealing operation. Although not shown in the drawings, each of the platen is embedded with a plurality of electric heating coils which raise the platens, which are constructed of a high heat capacity material, to the elevated temperatures which are required for rapidly and effectively melting the plastic utilized in the battery cases. Therefore, since it is necessary for workmen desiring to change the platen to work in close proximity to the platen when unbolting the platen from the carriage, it is necessary for safety reasons to allow a platen previously in use to cool. Once the platen previously in use has cooled to a sufficient temperature to allow safe working, that battery platen must be manually unbolted and removed for storage in a location which is protected from any influences which might disturb the melting portions inscribed on the surfaces of the platen. Then the new platen to be mounted on the machine must be manually bolted onto the carriage and the first attempt at aligning the platen is then made. Unfortunately, it is not possible to determine the success of the preliminary alignment operation until the platen has reached an operating temperature. At this time, various samples may be run through the machine to determine the effectiveness of the prealignment. In most instances, the high heat capacity of the platen which is employed, together with the thermal output of the electric heating elements embedded therein, require at least 1 hour to bring the platen to operating temperature. At that point, if it appears that the prealignment operation was not successful in properly aligning the platen with respect to the battery cases and covers to be sealed, it is then necessary to again adjust the position of the platen with respect to the carriage. Unfortunately, at this point, either the platen must be allowed to cool again or attempts must be made to align the platen while it is still in the heated condition. Neither of these methods being ideal, a somewhat less than satisfactory compromise is usually decided upon which, if successful, reduces somewhat the number of hours which must be expended in aligning the platen prior to returning to production.
The above described problems are particularly severe when encountered in the production environment normally present in all but the largest battery production facilities. In particular, since batteries are made in a wide variety of shapes and sizes, and since a single, modern production facility may produce several thousand batteries from one production line in a single working day, the inability of prior art heat sealing machines to rapidly change from one platen to the next effectively limits the productivity of an entire battery production line. In order to maintain maximum production, it has heretofore been necessary to schedule excessive amounts of overtime and/or to stock large volumes of batteries in inventory in order to minimize the necessity of changing from one platen configuration to another. Furthermore, since a certain amount of speed can be gained by taking certain safety risks with respect to handling the hot platen, the present method and apparatus employed in mounting and changing platens is, at best, somewhat less than desirable.